According to a new study, immigrants who come to the United States from Mexico arrive with a significant amount of undiagnosed disease.
This tempers previous findings that immigrants are generally healthier than native-born residents.
About half of recent Mexican immigrants who have diabetes are unaware they have the disease and about one-third of those with high blood pressure are unaware of the illness, according to findings published in the December edition of the journal Health Affairs
The undiagnosed disease explains about one-third of the "healthy immigrant effect" for diabetes and one-fifth for high blood pressure. But even after undiagnosed disease is taken into account, recent immigrants are still healthier than native-born residents.
"Our findings show that Mexican immigrants to the United States are not as healthy as previously thought when undiagnosed disease -- particularly diabetes -- is taken in account," said James P. Smith, the study's senior author and a senior economist at RAND, a nonprofit research organization.
Co-authors of the study are Silvia Helena Barcellos of RAND and Dana Goldman of USC.
Past research has established the phenomena known as the health immigrant effect. Compared to native-born Americans, Mexican immigrants arriving in the United States report being in better health, although that advantage disappears the longer they stay in the United States.
One explanation for the healthy immigrant effect is that those who migrated to the United States, usually to seek employment, are more likely to be younger and healthy than the overall population. But since immigrants often arrive from countries that have poor access to health services, researchers wanted to examine whether immigrants might only report better health than the native born.
The RAND study was done by examining information for people aged 30 to 60 from the National Health and Nutrition Examination Survey for the periods 1988 to 1994 and 1999 to 2008. The survey polls a large group of people nationally, assessing health status through comprehensive physical exams and laboratory tests in addition to asking participants about their health.
The study confirmed what has been shown by other studies -- Mexican immigrants in the United States for fewer than five years report being in much better health on arrival than their native-born American counterparts. When the clinical examinations were considered, the gap between the two groups closed somewhat.
Immigrants who had been in the United States four years or less were about twice as likely to have undiagnosed diabetes as compared to those who had been in the country for 15 years or more. In total, 59 percent of recent Mexican immigrants who had diabetes were undiagnosed, as were 33 percent of those Mexican immigrants who had high blood pressure.
"A lack of disease awareness is clearly a serious problem among recent Mexican immigrants," said Barcellos, a RAND economist. "Our findings underscore the importance of screening recent immigrants for illnesses to avoid late diagnosis and any potential costs of delayed treatment."
The study found the prevalence of diabetes was higher among Mexican Americans and Mexican immigrants than among native-born Americans who were not of Mexican descent, indicating that Mexicans generally have a higher risk for diabetes.